The Role of Auxin in the Polar Organisation of Apical Meristems

1993 ◽  
Vol 20 (5) ◽  
pp. 541 ◽  
Author(s):  
T Sachs
Keyword(s):  
Leaf Development ◽  
Direct Contact ◽  
Cell Shape ◽  
Cellular Level ◽  
Vascular Differentiation ◽  
Pisum Sativum L ◽  
Stem Internode ◽  
Young Leaves ◽  
Lower Stem

Auxin is a correlative signal, coordinating leaf development with vascular differentiation and other developmental processes throughout the plant. It has a unique influence on the orientation of the differentiation of the cambium and its products. The problem considered was whether auxin has similar correlative roles in the development of meristematic stems. Seedlings of Pisum sativum L. were decapitated and the buds in the axil of the lower bract were used in all experiments. The lower stem internodes of these buds were ≤ 2 mm long and grew to about 50 mm in 6 d. The elongation of a stem internode continued even in the absence of all young leaves. However, vascular differentiation and transverse parenchyma growth correlated with the presence of developing leaves. Auxin replaced leaf effects on all stem tissues. The influence of both leaves and auxin were limited to the direction of the roots and to the sectors of the stem below the point of auxin application. This polarity differed from that of more mature tissues in requiring a direct contact with the roots. Another characteristic of minute stem internodes was that changes of orientation, expressed by cell shape and the axis of vascular differentiation, did not occur readily. However, at a narrow competence window local hormone applications did cause the formation of new stem-like axes. It is concluded that auxin is a correlative signal even within shoot apices and that the information it carries has an essential directional com- ponent. This directionality has not been studied at the cellular level.

Sorbitol Versus Sucrose as Photosynthesis and Translocation Products in Developing Apricot Leaves

1985 ◽  
Vol 12 (6) ◽  
pp. 657 ◽  
Author(s):  
RL Bieleski ◽  
RJ Redgwell
Keyword(s):  
Leaf Development ◽  
Main Product ◽  
Mature Leaf ◽  
Young Leaf ◽  
Mature Leaves ◽  
Specific Transport ◽  
Young Leaves

Very young apricot leaves behave like the young leaves of most plants; that is, [14C]sucrose is formed as the main product of 14CO2 photosynthesis, and also when the leaves are supplied with [14C]glucose. [14C]sorbitol is not produced, and is poorly metabolized when fed to the leaf. Expanding leaves behave differently: [14C]sorbitol and [14C]sucrose are formed in similar amounts from both 14CO2 and [14C]glucose; and when [14C]sorbitol is supplied, it is readily metabolized and utilized for growth. Mature leaves are different again. They form [14C]sorbitol as the main product from 14CO2 and from [14C]glucose, and they do not metabolize [14C]sorbitol at all. Thus during development, apricot leaves gain but then lose the ability to utilize sorbitol. They also gain and keep the ability to synthesize sorbitol. This suggests that different biochemical paths exist for sorbitol formation and utilization, and that these paths are differently developed in the various stages of leaf development. Although the very young leaves did not synthesize sorbitol from CO2 or glucose, they contained it as their major sugar. Translocation behaviour was therefore studied. Neither the very young leaves nor the expanding leaves export any photosynthate, but the mature leaf rapidly translocates carbohydrate, mainly in the form of sorbitol, to the younger leaves as well as the rest of the plant. [14C]sorbitol supplied to the mature leaf can be recovered in that form from the very young leaf on the same shoot. This further establishes the role of sorbitol in apricot as a specific transport carbohydrate.

The dense indumentum with its polyphenol content may replace the protective role of the epidermis in some young xeromorphic leaves

1996 ◽  
Vol 74 (3) ◽  
pp. 347-351 ◽  
Author(s):  
George Karabourniotis ◽  
Costas Fasseas
Keyword(s):  
Radiation Damage ◽  
Leaf Development ◽  
Olea Europaea ◽  
Quercus Ilex ◽  
Developmental Stages ◽  
Protective Role ◽  
Ultraviolet B ◽  
Young Leaves ◽  
Olea Europaéa

The bright, yellow-green, ammonia-induced fluorescence of polyphenol compounds contained in the nonglandular hairs and within the epidermis of Olea europaea and Quercus ilex leaves was age dependent. Epifluorescence microscopic examination of transverse sections of leaves from both species showed that abaxial and adaxial epidermal layers emitted the characteristic green-yellow bright fluorescence only in late developmental stages, when a considerable decrease of the trichome density had already occurred. At earlier developmental stages, only the dense and thick trichome layer emitted the bright green-yellow fluorescence. In addition, the trichomes of young leaves of Olea and Quercus resembled the glandular ones of other species morphologically and possibly functionally. These findings suggest that the protective role of the trichome against ultraviolet-B radiation damage and (or) other environmental factors is particularly significant during the early stages of leaf development and may be less important at later stages, when the protective role is taken over by the epidermis. Keywords: leaf hairs, phenolics, UV-B radiation damage, leaf development, Olea europaea L., Quercus ilex L.

scholarly journals EpCAM promotes endosomal modulation of the cortical RhoA zone for epithelial organization

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Cécile Gaston ◽  
Simon De Beco ◽  
Bryant Doss ◽  
Meng Pan ◽  
Estelle Gauquelin ◽  
...  
Keyword(s):  
Cell Shape ◽  
Specific Protein ◽  
Cell Polarization ◽  
Stress Fiber ◽  
Fiber Formation ◽  
Endosomal Trafficking ◽  
Transient Zone ◽  
And Behavior ◽  
Fine Tune

AbstractAt the basis of cell shape and behavior, the organization of actomyosin and its ability to generate forces are widely studied. However, the precise regulation of this contractile network in space and time is unclear. Here, we study the role of the epithelial-specific protein EpCAM, a contractility modulator, in cell shape and motility. We show that EpCAM is required for stress fiber generation and front-rear polarity acquisition at the single cell level. In fact, EpCAM participates in the remodeling of a transient zone of active RhoA at the cortex of spreading epithelial cells. EpCAM and RhoA route together through the Rab35/EHD1 fast recycling pathway. This endosomal pathway spatially organizes GTP-RhoA to fine tune the activity of actomyosin resulting in polarized cell shape and development of intracellular stiffness and traction forces. Impairment of GTP-RhoA endosomal trafficking either by silencing EpCAM or by expressing Rab35/EHD1 mutants prevents proper myosin-II activity, stress fiber formation and ultimately cell polarization. Collectively, this work shows that the coupling between co-trafficking of EpCAM and RhoA, and actomyosin rearrangement is pivotal for cell spreading, and advances our understanding of how biochemical and mechanical properties promote cell plasticity.

scholarly journals The role of JrPPOs in the browning of walnut explants

2021 ◽  
Vol 21 (1) ◽  
Author(s):  
Shugang Zhao ◽  
Hongxia Wang ◽  
Kai Liu ◽  
Linqing Li ◽  
Jinbing Yang ◽  
...  
Keyword(s):  
Tissue Culture ◽  
Production Efficiency ◽  
Phenolic Content ◽  
Leaf Tissue ◽  
Limiting Factor ◽  
Mature Leaves ◽  
Survival Percentage ◽  
Highly Active ◽  
Young Leaves

Abstract Background Tissue culture is an effective method for the rapid breeding of seedlings and improving production efficiency, but explant browning is a key limiting factor of walnut tissue culture. Specifically, the polymerization of PPO-derived quinones that cause explant browning of walnut is not well understood. This study investigated explants of ‘Zanmei’ walnut shoot apices cultured in agar (A) or vermiculite (V) media, and the survival percentage, changes in phenolic content, POD and PPO activity, and JrPPO expression in explants were studied to determine the role of PPO in the browning of walnut explants. Results The results showed that the V media greatly reduced the death rate of explants, and 89.9 and 38.7% of the explants cultured in V media and A media survived, respectively. Compared with that of explants at 0 h, the PPO of explants cultured in A was highly active throughout the culture, but activity in those cultured in V remained low. The phenolic level of explants cultured in A increased significantly at 72 h but subsequently declined, and the content in the explants cultured in V increased to a high level only at 144 h. The POD in explants cultured in V showed high activity that did not cause browning. Gene expression assays showed that the expression of JrPPO1 was downregulated in explants cultured in both A and V. However, the expression of JrPPO2 was upregulated in explants cultured in A throughout the culture and upregulated in V at 144 h. JrPPO expression analyses in different tissues showed that JrPPO1 was highly expressed in stems, young leaves, mature leaves, catkins, pistils, and hulls, and JrPPO2 was highly expressed in mature leaves and pistils. Moreover, browning assays showed that both explants in A and leaf tissue exhibited high JrPPO2 activity. Conclusion The rapid increase in phenolic content caused the browning and death of explants. V media delayed the rapid accumulation of phenolic compounds in walnut explants in the short term, which significantly decreased explants mortality. The results suggest that JrPPO2 plays a key role in the oxidation of phenols in explants after branch injury.

scholarly journals Minireview: Thyroid Hormone Transporters: The Knowns and the Unknowns

2011 ◽  
Vol 25 (1) ◽  
pp. 1-14 ◽  
Author(s):  
W. Edward Visser ◽  
Edith C. H. Friesema ◽  
Theo J. Visser
Keyword(s):  
Thyroid Hormone ◽  
Organic Anion ◽  
Psychomotor Retardation ◽  
Cellular Level ◽  
Monocarboxylate Transporter ◽  
Causative Role ◽  
Organic Anion Transporting Polypeptide ◽  
Neurological Abnormalities ◽  
Knockout Animals

The effects of thyroid hormone (TH) on development and metabolism are exerted at the cellular level. Metabolism and action of TH take place intracellularly, which require transport of the hormone across the plasma membrane. This process is mediated by TH transporter proteins. Many TH transporters have been identified at the molecular level, although a few are classified as specific TH transporters, including monocarboxylate transporter (MCT)8, MCT10, and organic anion-transporting polypeptide 1C1. The importance of TH transporters for physiology has been illustrated dramatically by the causative role of MCT8 mutations in males with psychomotor retardation and abnormal serum TH concentrations. Although Mct8 knockout animals have provided insight in the mechanisms underlying parts of the endocrine phenotype, they lack obvious neurological abnormalities. Thus, the pathogenesis of the neurological abnormalities in males with MCT8 mutations is not fully understood. The prospects of identifying other transporters and transporter-based syndromes promise an exciting future in the TH transporter field.

EB1 Is Essential for Spindle Formation and Chromosome Alignment During Oocyte Meiotic Maturation in Mice

2021 ◽  
pp. 1-7
Author(s):  
Dongjie Zhou ◽  
Zheng-Wen Nie ◽  
Xiang-Shun Cui
Keyword(s):  
Cell Shape ◽  
Control Cell ◽  
Meiotic Maturation ◽  
Junctional Complex ◽  
Spindle Formation ◽  
Oocyte Meiosis ◽  
Polarized Cell Growth ◽  
Chromosome Alignment ◽  
Oocyte Meiotic Maturation

The cytoskeleton plays an orchestrating role in polarized cell growth. Microtubules (MTs) not only play critical roles in chromosome alignment and segregation but also control cell shape, division, and motility. A member of the plus-end tracking proteins, end-binding protein 1 (EB1), regulates MT dynamics and plays vital roles in maintaining spindle symmetry and chromosome alignment during mitosis. However, the role of EB1 in mouse oocyte meiosis remains unknown. Here, we examined the localization patterns and expression levels of EB1 at different stages. EB1 protein level was found to be stable during meiosis. EB1 mainly localized along the spindle and had a similar localization pattern as that of α-tubulin. The EB1 protein was degraded with a Trim-Away method, and the results were further confirmed with western blotting and immunofluorescence. At 12 h of culture after EB1 knockdown (KD), a reduced number of mature MII oocytes were observed. EB1 KD led to spindle disorganization, chromosome misalignment, and missegregation; β-catenin protein binds to actin via the adherens junctional complex, which was significantly reduced in the EB1 KD oocytes. Collectively, we propose that the impairment of EB1 function manipulates spindle formation, thereby promoting chromosomal loss, which is expected to fuel aneuploidy and possibly fertilization failure.

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